The present invention relates to a semiconductor device and, more particularly, to a semiconductor device incorporating means for identifying the state of the device.
For example, in a semiconductor memory device, a large number of memory cells are arranged along rows and columns which are orthogonal to each other. A density of defects generated in such a semiconductor memory device during the manufacture thereof is relatively independent of the integration density of the device, but is dependent on semiconductor manufacturing technology. Therefore, the higher the integration density of the device, the greater the ratio of the number of normal memory cells to that of defective memory cells. This is one of the advantages obtained by increasing the integration density of a semiconductor memory device. However, even if the device includes only one defective memory cell, the device cannot be operated normally and, therefore, the device must be abandoned.
In order to be able to operate a semiconductor memory device despite such a defective memory cell, a semiconductor memory device has been known in which a redundancy memory cell array is incorporated with a main memory cell matrix along the rows or the columns thereof. In this device, when a defective memory cell is detected, the redundancy memory cell array is used instead of a row memory cell array or a column memory cell array which includes a defective memory cell. Therefore, in a semiconductor memory device by incorporating a redundancy memory cell array, the manufacturing yield can be improved.
In such a semiconductor memory device incorporating a redundancy memory cell array, from the point of view of quality control, it is important to know whether or not the redundancy memory cell array is being used. One approach is to provide a bit ROM (read only memory) of a fuse type which serves as a flag register. If the redundancy memory cell array is used, "0" is written into the ROM, while, if the redundancy memory cell array is not used, "1" is written into the ROM. However, in order to read information stored in the ROM, terminals therefor must be provided in the device, so that the device becomes large.
It should be noted that such information stored in the ROM is rarely read out; that is, the information is read out only during the check mode.